Datasheet

14.3.2.2 General Write synchronization
Write-Synchronization is triggered by writing to a register in the peripheral clock domain. The respective
bit in the Synchronization Busy register (SYNCBUSY) will be set when the write-synchronization starts
and cleared when the write-synchronization is complete. Refer to 14.3.2.7 Synchronization Delay for
details on the synchronization delay.
When write-synchronization is ongoing for a register, any subsequent write attempts to this register will be
discarded, and an error will be reported.
Example:
REGA, REGB are 8-bit peripheral core registers. REGC is 16-bit peripheral core register.
Offset Register
0x00 REGA
0x01 REGB
0x02 REGC
0x03
Synchronization is per register, so multiple registers can be synchronized in parallel. Consequently, after
REGA (8-bit access) was written, REGB (8-bit access) can be written immediately without error.
REGC (16-bit access) can be written without affecting REGA or REGB. If REGC is written to in two
consecutive 8-bit accesses without waiting for synchronization, the second write attempt will be discarded
and an error is generated.
A 32-bit access to offset 0x00 will write all three registers. Note that REGA, REGB and REGC can be
updated at different times because of independent write synchronization.
14.3.2.3 General read synchronization
Read-synchronized registers are synchronized when the register value is updated. During
synchronization the corresponding bit in SYNCBUSY will be set. Reading a read-synchronized register
will return its value immediately and the corresponding bit in SYNCBUSY will not be set.
14.3.2.4 Completion of synchronization
In order to check if synchronization is complete, the user can either poll the relevant bits in SYNCBUSY
or use the Synchronisation Ready interrupt (if available). The Synchronization Ready interrupt flag will be
set when all ongoing synchronizations are complete, i.e. when all bits in SYNCBUSY are '0'.
14.3.2.5 Enable Write-Synchronization
Setting the Enable bit in a module's Control register (CTRL.ENABLE) will also trigger write-
synchronization and set SYNCBUSY.ENABLE. CTRL.ENABLE will read its new value immediately after
being written. SYNCBUSY.ENABLE will be cleared by hardware when the operation is complete. The
Synchronisation Ready interrupt (if available) cannot be used for Enable write-synchronization.
14.3.2.6 Software Reset Write-Synchronization
Setting the Software Reset bit in CTRLA (CTRLA.SWRST=1) will trigger write-synchronization and set
SYNCBUSY.SWRST. When writing a ‘1’ to the CTRLA.SWRST bit it will immediately read as ‘1’.
CTRL.SWRST and SYNCBUSY.SWRST will be cleared by hardware when the peripheral has been reset.
Writing a '0' to the CTRL.SWRST bit has no effect. The Ready interrupt (if available) cannot be used for
Software Reset write-synchronization.
SAM D21 Family
Clock System
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 114